Disk array apparatus and control method for disk array apparatus

ABSTRACT

Resources of a storage apparatus are utilized effectively by increasing and reducing a capacity of a differential LU used in a snapshot. In a disk array apparatus including a control processor which controls reading and writing of data with respect to a first logical volume which is generated using storage areas of a plural disk drives, performs control such that data in the past stored in the first logical volume is written in a second logical volume as differential data for each generation, and manages the differential data, the control processor manages a pool management table, in which a logical volume usable as the second logical volume is registered, and a pool addition object management table, in which a logical volume which can be added to the second logical volume is registered, and moves the logical volume from the pool addition object management table to the pool management table to thereby increase a capacity of the second logical volume.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of application Ser. No.10/855,421, filed May 28, 2004, now U.S. Pat. No. 7,139,875, whichclaims priority from Japanese Patent Application No. 2004-114189, filedon Apr. 8, 2004, the entire disclosure of which is incorporated hereinby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a disk array apparatus, and inparticular to a management technique for a differential LU in asnapshot.

2. Description of the Related Art

In a computer system, a copy of a storage volume storing original datamay be generated, for example, in the case in which data to be stored ina storage device is backed up. In this case, the storage volume storingoriginal data and a storage volume storing copy data are required tohave the same contents and keep consistency. Thus, it is necessary tostop update of the storage volume storing original data until generationof the copy is completed. However, in a computer system or the like inwhich high-availability is required, access to the storage volumestoring original data cannot be stopped in some cases.

Therefore, a technique called snapshot has been developed. The snapshotkeeps consistency at a certain point in time between the storage volumestoring original data and the storage volume storing copy data such thatthe original data at a point in time can be referred to even if theoriginal data is updated after the point in time (See JP-A-2001-306407).

According to the technique of snapshot, in the case in which theoriginal data is updated after the point when consistency should bekept, the data at the point when consistency should be kept is stored inanother storage volume. In other words, the original data is kept as itis unless it is updated, and the data at the point when consistencyshould be kept is stored in another storage volume as differential dataif it is updated.

Although a snapshot function has an advantage that a capacity of adifferential LU can be reduced compared with a capacity of a primary LU,differential data increases if an amount of data to be written from ahost increases. Then, when utilization of the differential LU hasreached 100%, the snapshot cannot be maintained. Consequently, if alarge number of LUs are set as differential LUs, the LUs cannot be usedfor other applications in the case in which a large amount of data isnot written.

SUMMARY OF THE INVENTION

It is an object of the present invention to increase and reduce acapacity of a differential LU, which is used in a snapshot, to therebyutilize resources of a storage device effectively.

The present invention provides a disk array apparatus which comprises: ahost interface which is connected to a host apparatus and receives datafrom the host apparatus; a memory which is connected to the hostinterface and stores data to be exchanged with the host apparatus andcontrol information on the data to be exchanged with the host apparatus;plural disk interfaces which are connected to the memory and performcontrol such that the data to be exchanged with the host apparatus isread from and written in the memory; plural disk drives which areconnected to the plural disk interfaces and in which the data sent fromthe host apparatus is stored under the control of the plural diskinterfaces; and a control processor which controls reading and writingof data with respect to a first logical volume which is generated usingstorage areas of the plural disk drives, performs control such that datain the past stored in the first logical volume is written in a secondlogical volume as differential data for each generation, and manages thedifferential data by providing a snapshot management table for managingthe differential data in an area of the memory. In the disk arrayapparatus, the control processor manages a pool management table, inwhich a logical volume usable as the second logical volume isregistered, and a pool addition object management table, in which alogical volume which can be added to the second logical volume isregistered, and moves the logical volume from the pool addition objectmanagement table to the pool management table to thereby increase acapacity of the second logical volume.

According to the present invention, resources of a storage apparatus canbe utilized effectively by increasing and reducing a capacity of LUsregistered in a pool area.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a diagram showing a structure of a disk array apparatus in anembodiment of the present invention;

FIG. 2 is an explanatory diagram of a control program in the embodimentof the present invention;

FIG. 3 is an explanatory diagram of a management method for adifferential LU in the embodiment of the present invention;

FIG. 4 is a flowchart of LU addition processing in a first embodiment ofthe present invention;

FIG. 5 is an explanatory diagram of the LU addition processing in thefirst embodiment of the present invention;

FIG. 6 is an explanatory diagram of a pool management table in a secondembodiment of the present invention;

FIG. 7 is a flowchart of LU addition processing in the second embodimentof the present invention;

FIG. 8 is an explanatory diagram of the LU addition processing in thesecond embodiment of the present invention;

FIG. 9 is an explanatory diagram of a pool management table in a thirdembodiment of the present invention;

FIG. 10 is a flowchart of LU deletion processing in the third embodimentof the present invention; and

FIG. 11 is an explanatory diagram of the LU deletion processing in thethird embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be hereinafter described withreference to the accompanying drawings.

FIG. 1 is a block diagram showing a structure of a disk array apparatusin an embodiment of the present invention.

A disk array apparatus 1 in the embodiment of the present inventionincludes a disk array controller 10 and disks 20. In addition, the diskarray apparatus 1 is connected to plural hosts 3 via a SAN 2 andconnected to a management terminal apparatus 5 via a LAN 4.

The disk array controller 10 controls input and output of data withrespect to the disks 20 according to operations of a control program103. In addition, a RAID (Redundant Array of Independent Disks) isconstituted by the disks 20 to give redundancy to data to be stored.Consequently, stored data is not lost even if a failure occurs in a partof the disks.

The disk array controller 10 includes a CPU 101, a memory 102, a datatransfer controller 104, a front-end interface 105, a back-end interface106, a cache memory 107, and a LAN interface 108.

The control program 103 (see FIG. 2) is stored in the memory 102. TheCPU 101 reads out and executes the control program 103, whereby variouskinds of processing are performed.

The data transfer controller 104 transfers data among the CPU 101, thefront-end interface 105, the back-end interface 106, and the cachememory 107.

The front-end interface 105 is an interface to the SAN 2, and sends andreceives data and control signals to and from the hosts 3, for example,according to a fiber channel protocol.

The back-end interface 106 is an interface to the disks 20, and sendsand receives data and control signals to and from the disks 20, forexample, according to the fiber channel protocol.

The cache memory 107 includes a cache in which data to be sent andreceived between the front-end interface 105 and the back-end interface106 is temporarily stored.

The data transfer controller 104 transfers data, which is read from andwritten in the disks via the SAN 4, between the interfaces 105 and 106.Moreover, the data transfer controller 104 transfers the data, which isread from and written in these disks, to the cache memory 107. Also,into the cache memory 107, the management tables 141 to 146 describedbelow are also recorded.

The LAN interface 108 is an interface to the LAN 4, and can send andreceive data and control signals to and from the management terminal 5,for example, according to a TCP/IP protocol.

The SAN 2 is a network which is capable of performing communicationaccording to a protocol suitable for transfer of data such as the fiberchannel protocol.

The host 3 is a computer apparatus including a CPU, a memory, a storage,an interface, an input device, and a display device, and makes itpossible to use a database service, a web service, and the likeutilizing data to be provided from the disk array apparatus 1.

The LAN 4 is used for management of the disk array apparatus 1 and iscapable of communicating data and control information among computers,for example, according to the TCP/IP protocol. For example, Ethernet(registered trademark) is used as the LAN 4.

The management terminal apparatus 5 is a computer apparatus including aCPU, a memory, a storage, an interface, an input device, and a displaydevice. A management program is operating in the management terminalapparatus 5. The management terminal apparatus 5 grasps an operationstate of the disk array apparatus 1 and controls the operation of thedisk array apparatus 1 according to the management program. Note that itis also possible that a client program such as a Web browser isoperating in the management terminal apparatus 5, and the operation ofthe disk array apparatus 1 is controlled according to a managementprogram which is supplied from the disk array apparatus 1 by a CGI(Common Gateway Interface) or the like.

FIG. 2 is an explanatory diagram of the control program 103 in theembodiment of the present invention.

A data input/output request sent from a normal I/O processing program301 of the host 3 is analyzed by an R/W command analysis program 111 ofthe control program 103 of the disk array apparatus 1 and sent to a snapjob program 121.

Upon receiving a request for writing data in a primary LU, the snap jobprogram 121 copies data before update in the primary LU to adifferential LU and updates contents of the primary LU after thiscopying. Moreover, the snap job program 121 updates a snapshotmanagement table (a differential information management block 204) suchthat blocks in a virtual LU corresponding to blocks in the primary LU,in which the data is updated, are associated with blocks on thedifferential LU in which the data of the primary LU at a point ofreception of a snapshot generation request (i.e., the data beforeupdate) is stored.

In addition, upon receiving a request for access to the virtual LU, asnap restore job program 122 accesses the blocks in the primary LU orthe blocks in the differential LU, which are associated with the blocksin the virtual LU, with reference to the snapshot management table. Thismakes it possible for the disk array apparatus 1 to provide a snapshotimage. Then, the host 3 can utilize information in the primary LU at thepoint of the issuance of the snapshot generation request by accessingthe virtual LU according to the normal I/O processing program 301.

A control command sent from the normal I/O processing program 301 isanalyzed by an other command analysis program 112 and sent to aconfiguration information control program 170.

Upon receiving a snapshot generation request, first, a pair informationmanagement program 171 of the configuration information control program170 registers identification information for a new virtual LU in thesnapshot management table, and reserves and initializes a differentialbit map 202, a primary LU address table 203, and a differentialinformation management block 204. Blocks of this virtual LU areassociated with the blocks of the primary LU in a one-to-one relationaccording to the snapshot management table at first.

As described later, a pool LU management program 172 manages additionand deletion of LUs registered in a pool area.

A pool management program 150 performs management of reservation andrelease of an area in the snapshot differential management table(differential information management block 204), transition to an unusedqueue, and the like.

A WEB program 160 provides a WEB browser with a state of each paircreated in snapshot (presence or absence of a failure in a pair obtainedfrom information or the like in a pair information management table).

A RAID manager program 131 of the control program 103 of the disk arrayapparatus 1 is connected to a RAID manager program 302 of the host 3 soas to be capable of communicating with each other. Generation of asnapshot, change of a pair state, and the like can be performedaccording to the RAID manager programs 121 and 302.

In addition, a DAMP interface program 132 provides a user interfacewhich performs various kinds of setting for a disk array such asdeletion processing of a virtual LU. The DAMP interface program 122 isconnected to a DAMP program 501 of the management terminal apparatus 5so as to be capable of communicating with each other. Communication withthe DAMP program 501 of the management terminal apparatus 5 is performedby this DAMP interface program 122, whereby setting for management of aconfiguration of the RAID of the disk array apparatus 1, and automaticaddition and deletion of LUs in a pool is performed.

FIG. 3 is an explanatory diagram of a management method for snapshot inthe embodiment of the present invention.

A primary LU 201 is a logical unit (P-VOL: Primary Volume) which isserved for a normal operation and becomes an object of data input andoutput to and from the host 3.

The differential bit map 202 is provided in a management area of thecache memory 107 and has bits corresponding to blocks of the primary LU201 (e.g., 64 k bytes/block). This differential bit map 202 constitutesthe snapshot management table together with the primary LU address table203 and a differential information management block 204 to be describedlater.

In the case in which differential data corresponding to a block addressof the primary LU 201 is recorded in a differential LU 206, bits in thedifferential bit map 202 corresponding to the primary LU 201 are “1”.Therefore, when writing with respect to the primary LU 201 is performed,it can be judged if it is necessary to copy data before update to thedifferential LU 206 by referring to the differential bit map 202 (thatis, if bit are “1”, since data at the time of generation of snapshot hasalready been written in the differential LU 206, it is unnecessary tocopy data of the primary LU 201 to the differential LU 206).

The primary LU address table 203 is provided in a management area of thecache memory 107. In the primary LU address table 203, addresses in thedifferential information management block 204 are recorded inassociation with bits in the differential bit map 202.

The differential information management block 204 has the same capacityas the differential LU 206 and is provided in the management area of thecache memory 107. The differential information management block 204 ispartitioned for each of the blocks of the differential LU 206 (e.g., 64k bytes/block), and a management table is provided in each of thepartitioned parts of the differential information management block 204.This management table records correspondence between differential datarecorded in a position corresponding to a block in the differential LU206 and a generation of snapshot data. In addition, if there is otherdifferential data corresponding to the block in the primary LU 201, themanagement table records information on a link to an address on thedifferential information management block 204 corresponding to thedifferential data. In other words, it is possible to refer todifferential data of plural generations by tracing addresses recorded inthe differential information management block 204.

Note that unused areas in the differential information management block204 are linked as an unused queue. An amount of this unused queue ismanaged by an unused queue counter 205 provided in the cache memory 107.

The differential LU 206 is constituted by the LUs registered in the poolarea. The data in the primary LU 201 at the time of creation of asnapshot is copied in this differential LU 206. It can be learned from ageneration management bit map in the differential information managementblock 204 which generation of differential data the data in thedifferential LU 206 corresponds to.

Thus, in writing data in the primary LU 201, first, it is judged withreference to the differential bit map 202 whether it is necessary tocopy data before update to the differential LU 206. Then, if acorresponding bit in the differential bit map 202 is “1”, it is judgedthat it is unnecessary to copy the data before update to thedifferential LU 206, and the data is written in the primary LU 201. Onthe other hand, if a corresponding bit in the differential bit map 202is “0”, the data is written in the primary LU 201 after the data beforeupdate is copied to the differential LU 206.

Then, a link address with respect to differential data, which is setanew, is set in a block in the differential information management block204 corresponding to a block in the primary LU 201. An address of theblock of the differential information management block 204 is set in aprimary LU address table if necessary. The corresponding bit in thedifferential bit map 202 is changed to “1”, and a generation managementbit map in the differential information management block 204, whichcorresponds to an address in the differential LU 206 in which the databefore update is written, is set. Moreover, since the unused queue inthe differential information management block 204 is used, the unusedqueue counter 205 is updated.

In addition, in accessing the virtual LU (V-VOL: Virtual Volume), anaddress in the differential information management block 204 isspecified according to a block address in the virtual LU to be an objectof access (equivalent to a block address in the primary LU 201) withreference to the primary LU address table 203, and it is specifiedwhether there is differential data of a generation of the object ofaccess according to a generation management bit map of the address inthe differential information management block 204. Then, if there isdifferential data of a desired generation, differential data is read outfrom an address in the differential LU 206 corresponding to the addressin the differential information management block 204 to provide an imageof data of the virtual LU. On the other hand, if there is nodifferential data of the desired generation, differential data of thedesired generation is searched with reference to a link address withrespect to the other differential data. Further, if no differential datais differential data of the desired generation, data currently recordedin the primary LU 201 is provided as data of the virtual LU.

FIG. 4 is a flowchart of LU addition processing in a first embodiment ofthe present invention. The LU addition processing is executed by thepool LU management program 172 when a writing request for data isreceived from the host 3.

First, the program checks an unused capacity (or an already usedcapacity) of a pool area (differential LU) with reference to the unusedqueue counter 205 (S101).

Next, the program compares the utilization of the pool area acquired instep S101 and a threshold value decided in advance to judge whether ornot the utilization of the pool area has exceeded the threshold value(S102). It is desirable to set this threshold value to about 70%allowing a margin such that the utilization of the pool area does notreach 100%. However, the threshold value can be changed according to anoperation state (e.g., an amount of a data input/output request) of astorage apparatus.

In addition, execution of new LU addition processing can be prevented bysetting a threshold value higher than a value at a normal time duringexecution of processing for adding an LU in the pool area (e.g., 75% asopposed to 70% at the normal time) regardless of the fact that LUaddition processing is being executed because the utilization of thepool area has exceeded the threshold value.

Then, if the utilization of the pool area has not exceeded the thresholdvalue, the program judges that it is unnecessary to add an LU and endsthis processing without adding an LU. On the other hand, if theutilization of the pool area has exceeded the threshold value, theprogram proceeds to step S103.

In step S103, the program judges whether or not LUs are registered in apool automatic addition object with reference to the pool automaticaddition object management table 143 (FIG. 5). If LUs are not registeredin the pool automatic addition object, since an LU to be added is notpresent, the program ends this processing without adding an LU. On theother hand, if LUs are registered in the pool automatic addition object,the program proceeds to step S104.

In step S104, the program judges whether or not the number of LUsregistered in the pool area have reached a maximum number with referenceto a pool management table 146 (FIG. 5). The maximum value the number ofregistrations in the pool area is decided according to a capacity of thepool management table 146. If the number of LUs registered in the poolmanagement table 146 has already reached the maximum number, since an LUcannot be added to the pool management table 146 anew, the program endsthis processing without adding an LU. On the other hand, if the numberof LUs registered in the pool management table 146 is less than themaximum number, the program proceeds to step S105.

In step S105, the program judges whether or not a space is present inthe management area of the cache memory 107. This is because it isnecessary to increase a capacity of the differential informationmanagement block 204 following the addition of an LU in the pool area.If no space is present in the management area of the cache memory 107,since the area in the differential information management block 204cannot be increased, the program ends this processing without adding anLU. On the other hand, if a space is present in the management area ofthe cache memory 107, the program proceeds to step S106.

When conditions for adding an LU have been confirmed by the processingof S102 to S105, the program deletes an LU to be moved from the poolautomatic addition object management table 143 and adds the LU in thepool management table 146 to make the LU usable as a differential LU(S106).

Plural LUs can be designated in the pool management table 146 in advanceas the LUs to be moved. This makes it possible to add LUs by a necessarynumber. For example, if ten LUs of 100 GB are registered, three LUs of100 GB are added in the pool area if a capacity of the pool area is 300GB short, and the remaining seven LUs can be used for otherapplications.

Thereafter, the program sets an address of an unused queue, which ispresent in the area of the differential information management block 204increased anew, in a last unused queue in the differential informationmanagement block 204 which has been present, and joins the unused queueincreased anew to the unused queue which has been present (S107).

Note that this LU addition processing is executed in the case in whichutilization of a pool area has exceeded a threshold value decided inadvance. However, it is also possible that a higher second thresholdvalue different from the threshold value is set, and when theutilization has exceeded this second threshold value, differential datastored in the pool area is deleted to immediately reserve an unusedcapacity of the pool area.

FIG. 5 is an explanatory diagram of LU addition processing in the firstembodiment of the present invention.

A virtual LU (LU2), which provides an image of data at the time ofgeneration of a snapshot, is provided with respect to a primary LU(LU0). This LU2 is a virtual logical unit which is constituted by dataof the primary LU and differential data present in a pool area. Inshort, when the LU2 is accessed, it is judged whether data to beaccessed is present in the primary LU or is the differential datapresent in the pool area to realize access to the differential LU.

As an LU to be added to the pool area, an LU registered in the poolautomatic addition object management table 143 (LU6 and LU7) is deletedfrom the pool automatic addition object management table 143 and addedin the pool management table 146. Consequently, the added LU can be usedas a differential LU.

In this way, in the first embodiment of the present invention, pluralLUs for increasing a capacity of the pool area are prepared in advance,and if utilization of the pool area has exceeded a certain thresholdvalue, an LU is automatically added to the pool area to increase thecapacity of the pool area and prevent the utilization of the pool areafrom reaching 100%. In addition, if the utilization of the pool area issmall and it is unnecessary to add an LU, the LU can be used for otherapplications. Thus, a capacity of disks can be utilized effectivelywithout registering an unnecessary disk as a pool area.

Next, a second embodiment of the present invention will be described.

Unlike the first embodiment, in the second embodiment of the presentinvention, a primary LU is divided into groups, and conditions foradding an LU in a pool area can be set for each of the groups.

FIG. 6 is an explanatory diagram of a pool management table of thesecond embodiment of the present invention.

The pool management table is divided into an area of a group 1 (141) andan area of a group 2 (142).

In addition, the pool management table includes an “objective primaryLU” column in which primary LUs serving as primary volumes areregistered, a “pool registration LU” column in which LUs, which havealready been registered in the pool area and used as differential LUs,are registered, a “pool automatic addition object LU” column in whichLUs, which are pool automatic addition objects, are registered, and a“pool automatic addition conditions” column in which conditions forautomatic addition of an LU in the pool area are registered. In otherwords, the pool management table defines which LU is added at whichtiming.

More specifically, LU0 and LU3 belong to the group 1 as primary LUs, andLU11 and LU12 have already been added in the pool area. LU31, LU32, andLU33 are registered as group pool automatic addition objects. In short,LUs, which can be added for each of the groups, are definedindividually, whereby a large quantity of LUs can be prevented frombeing added to the pool area for a specific group (specific primary LU).

In addition, since (2) is selected in the “pool automatic additionconditions” column of the group 1, an LU is added according toconditions set as conditions common to the groups. When separate foreach group of (1) is selected, a threshold value for addition of an LUcan be changed and defined for each of the groups. According to amaximum capacity of a pool area of each group of (3), a maximum quantityof LUs, which can be added to the group, can be defined, and a largequantity of LUs can be prevented from being added in the pool area for aspecific group (specific primary LU). By designating a remainingcapacity of automatic addition object LUs of (4), a large remainingcapacity is reserved when an LU is added in a specific group, and theremaining LUs can be added in the other groups.

In the pool management table described above, groups are provided inassociation with primary LUs. However, groups of LUs may be provided inassociation with the hosts 3 or may be provided in association withapplication programs operating in the hosts 3.

FIG. 7 is a flowchart of LU addition processing in the second embodimentof the present invention. The LU addition processing is executed by thepool LU management program 172 when a writing request for data isreceived from the host 3. The LU addition processing is executed foreach group.

First, the program checks an already used capacity of a pool area(differential LU) with reference to the unused queue counter 205 (S111)and confirms conditions for adding an LU (S112 to S115). This processingis the same as the LU addition processing (S101 to S105 in FIG. 4) inthe first embodiment.

Next, the program judges whether automatic addition conditions for LUsare common or individual (S116). If the automatic addition conditionsfor LUs are common, since individual conditions for the group are notset, the program shifts to step S120. On the other hand, if theautomatic addition conditions for LUs are individual, the programconfirms addition conditions for LUs set for the group.

First, the program selects an LU to be added to the group with referenceto the “pool automatic addition object LU” column of the pool managementtable 146 or the like (S117). The program checks a maximum capacity of apool area of the group to judge whether or not the maximum value isexceeded even if the LU selected in step S117 is added (S118). Then,when the maximum capacity of the pool area of the group is exceeded, theprogram judges that excessive LUs are allocated to the group, and endsthis processing without adding an LU. On the other hand, if the maximumcapacity of the pool area of the group is not exceeded, the programproceeds to step S119.

Next, in step S119, the program judges whether or not a remainingcapacity of the pool automatic addition object LUs does not decrease tobe less than a predetermined value even if the LU selected in step S117is added. If the remaining capacity of the pool automatic additionobject LUs has decreased to be less than the predetermined value, theprogram judges that operations of the other groups are affected, andends this processing without adding an LU. On the other hand, if theremaining capacity of the pool automatic addition object LUs is not lessthan the predetermined value, the program proceeds to step S120.

Thereafter, when conditions for adding an LU have been confirmed, theprogram deletes an LU to be moved from the pool automatic additionobject management table 143 and add the LU in the pool management table146 to make the LU usable as a differential LU (S120).

Thereafter, the program sets an address of an unused queue, which ispresent in an area of the differential information management block 204increased anew, in a last unused queue in the differential informationmanagement block 204 which has been present, and joins the unused queueincreased anew to the unused queue which has been present (S121).

FIG. 8 is an explanatory diagram of LU addition processing in the secondembodiment of the present invention.

A virtual LU (LU2), which provides an image of data at the time ofgeneration of snapshot, is provided with respect to a primary LU (LU0).Similarly, a virtual LU (LU4) is provided with respect to a primary LU(LU3), a virtual LU (LU6) is provided with respect to a primary LU(LU5), and a virtual LU (LU8) is provided with respect to a primary LU(LU7).

In addition, LUs to be added in a pool area are registered in the poolautomatic addition object management table 143. An LU31 to an LU33 aredeleted from the pool automatic addition object management table 143,the LU31 and the LU32 are added in the pool management table 146 of thegroup 1, and the LU 33 is added in the pool management table 142 of thegroup 2. Consequently, the added LUs can be used as differential LUs ofthe respective groups.

In this way, in the second embodiment of the present invention, pluralLUs are divided into groups, and a capacity of a pool area isautomatically increased by a unit of the group, whereby setting withvaried reliability for each group can be performed.

In addition, influence of data input/output from each host can bestopped locally. A pool area is managed by a unit of the disk arraycontroller 10. When the host 3 runs away, and data writing instructionsare continuously issued solely for LUs under the control of the host, acapacity of a pool area with respect to the LUs under the control of thehost increases rapidly, and the other LUs cannot maintain a snapshot.Consequently, the LUs are divided into plural groups, and conditions forpool automatic addition are set for each of the groups, whereby a largequantity of LUs can be prevented from being added in the pool area for aspecific group (specific primary LU).

Next, a third embodiment of the present invention will be described.

In the third embodiment of the present invention, the LUs, which areadded in the pool area in the second embodiment, are deleted. Note that,although the case in which the LUs are divided into groups will bedescribed as in the second embodiment, the third embodiment can also beapplied to the first embodiment by considering only one group.

FIG. 9 is an explanatory diagram of a pool management table in the thirdembodiment of the present invention.

The pool management table (for LU deletion) is divided into an area of agroup 1 (144) and an area of a group 2 (145). Note that, here, only thearea of the group 1 (144) will be described.

The pool management table (for LU deletion) includes a “pool deletionobject LU” column in which LUs, which are objects of deletion from apool area, are registered, and an “automatic deletion object” column inwhich conditions for automatic deletion from the pool area areregistered. In other words, the pool management table (for LU deletion)defines which LU is deleted at which timing.

More specifically, an order of deletion of LUs is defined so as todelete an LU 31 and an LU 12 in this order from the group 1. Note that,other than defining the order of deletion of LUs, it is also possible todelete the LUs in an order opposite to the order of registration of theLUs (i.e., from an LU registered last) or to delete the LUs in an orderof a size of the LUs registered in the pool area (e.g., an LU with asmall capacity is deleted preferentially, or an LU with a large capacityis deleted preferentially).

In addition, in the group 1, conditions for deletion of an LU aredecided such that an LU is deleted from the pool area if utilization ofthe pool area is less than 30% continuously for one week. Note that,other than judging deletion of an LU according to the utilization of thepool area, it is also possible that utilization of the pool area afterdeletion of the LU is estimated to judge whether the LU should bedeleted on the basis of a result of comparison of the estimatedutilization of the pool area after deletion of the LU and a set value.Note that a period for monitoring the utilization of the LU can be setarbitrarily.

FIG. 10 is a flowchart of LU deletion processing of a third embodimentof the present invention. The LU deletion processing is executed by thepool LU management program 172.

The pool LU management program 172 checks an already used capacity of apool area (differential LU) with reference to the unused queue counter205 at predetermined timing (S131). Next, the program comparesutilization of the pool area acquired in step S101 and a threshold valuedecided in advance to judge whether or not the utilization of the poolarea is less than the threshold value (S132). For example, the programchecks a value of the unused queue counter 205 every hour to judgewhether the utilization of the pool area is less than 30% for one weekcontinuously. Conditions for judging the threshold value or the like areregistered in the pool management table 144 or the like.

If the utilization of the pool area is not less than the thresholdvalue, the program judges that it is unnecessary to delete an LU, andends this processing. On the other hand, if the utilization of the poolarea is less than the threshold value, the program selects an LU to bedeleted (S133). The program selects the LU to be deleted with referenceto the pool management table 144 or the like. For example, if (1) anorder of LUs to be deleted is registered in the pool management table144, the LUs can be deleted in accordance with the order. The LUs canalso be deleted (2) in an order opposite to an order of registration ofthe LUs (i.e., an LU registered last is deleted first). The LUs can alsobe deleted in an order of a size of the LUs registered in the pool area(e.g., an LU with a small capacity is deleted preferentially, or an LUwith a large capacity is deleted preferentially).

Note that, in the case in which an LU is deleted according to aninstruction from an administrator rather than being deletedautomatically, an LU to be deleted are designated in this step S133.

Thereafter, the program searches unused queues of the deletion object LUand creates an unused bit map (S134). This unused bit map is referred toin data copy from the deletion object LU (S138) and is used for copyingonly a block (not an unused queue) in use. In addition, utilization ofthe deletion object LU (a data amount required to be copied from thedeletion object LU) can be found by creating the unused bit map.

Then, the program deletes the unused queues of the deletion object LUfrom the differential information management block 204 (S135). In otherwords, the program cancels links of addresses from unused queues of theother LUs to the deletion object LU to separate the unused queues of thedeletion object LU and the unused queues of the other LUs and preventthe unused queues of the deletion object LU from being allocated anew.

Then, the program locks areas used by the deletion object LU such thatdata is not updated anew (S136).

Then, the program reserves unused queues, which are necessary forcopying data from the deletion object LU, in LUs remaining in the poolarea after the deletion of the LU (S137). Thereafter, the program copiesthe data from the deletion object LU to the LUs remaining in the poolarea after the deletion of the LU (S138).

Thereafter, concerning the data copied from the deletion object LU, theprogram updates address information of the differential informationmanagement block 204 to be recorded in the primary LU address table 203and updates links of addresses from differential data to be recorded inthe differential information management block 204 (other differentialdata corresponding to the block of the primary LU 201) (S139).

Then, the program updates bits of an unused bit map concerning the blockfor which the data copy has ended (S140). This makes it possible tograsp a state of progress of copying.

Thereafter, when copying of all data ends, the program releases the lockof the areas used by the deletion object LU (S141). Then, the programdeletes the LU to be move from the pool management table and adds the LUin the pool automatic addition object management table (S142).

FIG. 11 is an explanatory diagram of LU deletion processing in the thirdembodiment of the present invention.

A virtual LU (LU2), which provides an image of data at the time ofgeneration of a snapshot, is provided with respect to a primary LU(LU0). Similarly, a virtual LU (LU4) is provided with respect to aprimary LU (LU3).

LUs to be added in a pool area are registered in the pool automaticaddition object management table 143. An LU is deleted from the poolmanagement table 144 of the group 1 and added in the pool automaticaddition object management table 143. Consequently, the deleted LU isadded in pool areas of the other groups to make it possible to use theLU as a differential LU of the other groups.

In this way, in the third embodiment of the present invention, since anLU registered in a pool area is moved to a pool automatic additionobject, the LU can be used for other applications, and resources can beutilized effectively.

In the case in which LUs more than a quantity actually required for apool area of snapshot are registered, or in the case in which an I/O ofa host (an application operating in a host) changes and a necessarycapacity of a pool area (differential LU) decreases, reduction of acapacity of the pool area is not considered in the conventionaltechnique. On the other hand, in the present invention, when an LUregistered in the pool area is moved to a pool automatic additionobject, since a currently used area is copied to an unused queue ofanother LU, and when all areas of a moving object LU has become unused,the LU is moved to the pool automatic addition object, the LU can beused for other applications. Thus, a disk capacity can be utilizedeffectively.

In addition, since the LU is moved from the pool area to the poolautomatic addition object with reference to setting conditions, the diskcapacity can be utilized effectively without troubling an administrator.

1. A disk array apparatus comprising: a host interface which isconnected to a host apparatus and receives data from the host apparatus;a memory which is connected to the host interface and stores data to beexchanged with the host apparatus and control information on the data tobe exchanged with the host apparatus; plural disk interfaces which areconnected to the memory and perform control such that the data to beexchanged with the host apparatus is read from and written in thememory; plural disk drives which are connected to the plural diskinterfaces and in which the data sent from the host apparatus is storedunder the control of the plural disk interfaces; and a control processorwhich controls reading and writing of data with respect to a firstlogical volume which is generated using storage areas of the plural diskdrives, performs control such that data, stored in the first logicalvolume prior to being updated by the writing of update data into thefirst logical volume, is copied and written in a second logical volumeas differential data for each generation, and manages the differentialdata by providing a snapshot management table, which manages a relationamong differential data for each generation stored in the second logicalvolume, in an area of the memory, wherein the control processor managesan amount of data stored in the second logical volume, and reduces thecapacity of the second logical volume if the amount of data stored inthe second logical volume has decreased to be less than a second ratioof the capacity of the second logical volume.
 2. A disk array apparatusaccording to claim 1, wherein the control processor manages a poolmanagement table, in which a logical volume usable as the second logicalvolume is registered, and a pool addition object management table, inwhich a logical volume which can be added in the second logical volumeis registered.
 3. A disk array apparatus according to claim 1, whereinthe control processor manages an amount of data stored in the secondlogical volume and reduces the capacity of the second logical volume tomake it possible to use a reduced capacity of the second logical volumein other applications.
 4. A disk array apparatus comprising: a hostinterface which is connected to a host apparatus and receives data fromthe host apparatus; a memory which is connected to the host interfaceand stores data to be exchanged with the host apparatus and controlinformation on the data to be exchanged with the host apparatus; pluraldisk interfaces which are connected to the memory and perform controlsuch that the data to be exchanged with the host apparatus is read fromand written in the memory; plural disk drives which are connected to theplural disk interfaces and in which the data sent from the hostapparatus is stored under the control of the plural disk interfaces; anda control processor which controls reading and writing of data withrespect to a first logical volume which is generated using storage areasof the plural disk drives, performs control such that data, stored inthe first logical volume prior to being updated by the writing of updatedata into the first logical volume, is copied and written in a secondlogical volume as differential data for each generation, and manages thedifferential data by providing a snapshot management table, whichmanages the differential data, in an area of the memory, wherein thecontrol processor manages a pool management table, in which a logicalvolume usable as the second logical volume is registered, and a pooladdition object management table, in which a logical volume which can beadded in the second logical volume is registered.
 5. A disk arrayapparatus according to claim 4, wherein the control processor manages anamount of data stored in the second logical volume, and reduces thecapacity of the second logical volume by adding or deleting a logicalvolume in the pool management table on the basis of a result ofcomparison of the amount of data stored in the second logical volume andthe capacity of the second logical volume.
 6. A disk array apparatusaccording to claim 5, wherein the control processor reduces the capacityof the second logical volume by deleting a logical volume from the poolmanagement table if the amount of data stored in the second logicalvolume is less than a second predetermined value continuously for apredetermined period.
 7. A disk array apparatus according to claim 5,wherein the control processor reduces the capacity of the second logicalvolume by deleting a logical volume from the pool management table ifthe amount of data stored in the second logical volume is less than athird predetermined value even if the second logical volume is deleted.8. A disk array apparatus according to claim 4, wherein, by dividing thepool management table into groups, the control processor manages thefirst logical volume and the second logical volume for each of thegroups, and reduces a capacity of the second logical volume of each ofthe groups by adding a new logical volume to or deleting a logicalvolume from the pool management table of each of the groups on the basisof a result of comparison of an amount of data stored in the secondlogical volume of each of the groups and the capacity of the secondlogical volume of the group.
 9. A disk array apparatus according toclaim 8, wherein the control processor adds a new logical volume in thepool management table of each of the groups if the capacity of thesecond logical volume of each of the groups does not exceed a secondpredetermined value even if the second logical volume is added.
 10. Adisk array apparatus according to claim 8, wherein the control processoradds a new logical volume in the pool management table of each of thegroups if a capacity of a logical volume, which can be added as thesecond logical volume, registered in the pool addition object managementtable does not decrease to be less than a third predetermined value evenif the second logical volume is added.
 11. A disk array apparatusaccording to claim 8, wherein the control processor reduces the capacityof the second logical volume of each of the groups by deleting a logicalvolume from the pool management table of each of the groups if theamount of data stored in the second logical volume of each of the groupshas decreased to be less than a fourth predetermined value set for thegroup.
 12. A control method in a disk array apparatus comprising: a hostinterface which is connected to a host apparatus and receives data fromthe host apparatus; a memory which is connected to the host interfaceand stores data to be exchanged with the host apparatus and controlinformation on the data to be exchanged with the host apparatus; pluraldisk interfaces which are connected to the memory and perform controlsuch that the data to be exchanged with the host apparatus is read fromand written in the memory; plural disk drives which are connected to theplural disk interfaces and in which the data sent from the hostapparatus is stored under the control of the plural disk interfaces; anda control processor which controls reading and writing of data withrespect to a first logical volume which is generated using storage areasof the plural disk drives, performs control such that data, stored inthe first logical volume prior to being updated by the writing of updatedata into the first logical volume, is copied and written in a secondlogical volume as differential data for each generation, and manages thedifferential data by providing a snapshot management table, whichmanages a relation among differential data for each generation stored inthe second logical volume, in an area of the memory, wherein the controlprocessor manages an amount of data stored in the second logical volume,manages a pool management table, in which a logical volume usable as thesecond logical volume is registered, and a pool addition objectmanagement table, in which a logical volume which can be added to thesecond logical volume is requested, and reduces the capacity of thesecond logical volume as needed.